A touch panel is a position input device which can detect a position indicated with a finger, a stylus, or the like and can generate a signal including the positional information. A display device which is obtained in such a manner that a touch panel overlaps with an image display area is referred to as a touch screen, and the display device can display an image in an image display region and can obtain as information which position in the image display region a user indicates. In addition, an example of a touch screen includes a touch screen in which a photoelectric conversion element called a photosensor is provided in an image display region and a position indicated by a user is detected by intensity of light. The touch screen has both functions as a position input device and as a display device; therefore, the touch screen has high operability and the size of an electronic device is easily reduced as compared to the case where a position input device such as a touchpad or a mouse is used.
An information display device having a touch panel and a liquid crystal display panel is described in Patent Document 1.